A purge and trap concentrator, such as the Tekmar-Dohrmann 3100 Sample Concentrator, receives a liquid sample that typically includes volatile compounds. When the purge and trap concentrator heats the liquid sample and passes a purge gas through it, volatile compounds are purged from the liquid as gas or vapor and are trapped in a trap. The trapped volatile compounds are then transferred to a gas chromatograph or other chemical analysis instrument for chemical analysis. There is a need to consistently dry the volatile compounds before they are transferred to the chemical analysis instrument. A lithium chloride dryer is typically used for drying the transferred volatile compounds.
In purge and trap applications, the lifetime of a dryer using lithium chloride is limited. The dryer is cycled repeatedly to absorb water, and then the dryer is baked to remove moisture before the dryer is returned to service in the purge and trap concentrator.
The lithium chloride is an inorganic salt that is very hygroscopic. Lithium chloride efficiently scavenges moisture from sample gas with which it comes in contact. When used alone, however, lithium chloride, tends to solidify or cake up as it accumulates water. The surface area of the lithium chloride is reduced with repeated use and baking. Eventually, lithium chloride tends to solidify so much that it blocks flow of the sample gas, and the efficiency of moisture removal is greatly reduced.
A purge and trap concentrator and method are needed that will extend the useful lifetime of lithium chloride for drying a stream of sample gas in a purge and trap concentrator.